The invention relates to electrical energy management systems that shed and restore prioritized controlled loads in such a manner as to minimize peaking of power consumption of a resistance with minimum impact on the life-style of residential occupants in order to maximize utility company revenue by keeping power consumption close to a level that utilizes as much as possible of the utility company's capacity to generate electrical power from hydroelectric, nuclear, coal-fired and other generating sources that have relatively low operating costs but require very large capital outlays to construct, thereby avoiding the need for the utility company to use oil or gas powered peak load generating sources that sharply increase the rates that must be charged to utility customers.
A number of power controllers or energy controllers useful for shedding and restoring controlled loads in a residence have been proposed, including those disclosed in commonly assigned copending applications "System and Method for Optimizing Shed/Restore Operations for Electrical Loads"Ser. No. 191,424, filed Sept. 26, 1980 by Hedges et al. and "System and Method for Optimizing Power/Shed Restore Operations", Ser. No. 274,488, filed June 17, 1981 by Gurr et al. Commonly assigned issued U.S. Pat. No. 4,247,786 are indicative of the state of the art. U.S. Pat. No. 3,652,838; U.S. Pat. No. 3,906,242; U.S. Pat. No. 4,023,043; U.S. Pat. No. 4,059,747; U.S. Pat. No. 4,064,485; U.S. Pat. No. 4,075,699; U.S. Pat. No. 4,146,923; U.S. Pat. No. 4,168,491; U.S. Pat. No. 4,181,950; and U.S. Pat. No. 4,216,384 also are believed to be generally indicative of the state of the art for energy controllers.
The various energy controllers disclosed in these references are intended to keep peak power usage by residential customers approximately below a predetermined level while maintaining the total cumulative amount of energy used by customers relatively unchanged, thereby postponing use of certain electrical loads when such postponing does not cause undue inconvenience to the residential customers.
Some of the energy controllers described in the above references are relatively complex, computer-controlled devices that utilize control panels by means of which the customer selects a peak limit to the amount of power that can be (instantaneously) consumed by the residence. The various loads that are controlled by the energy controllers are connected to the controller in order of relative priorities of the loads. The above-described energy controllers shed and restore loads in certain predetermined priorities in accordance with various shed/restore algorithyms executed by the computers in order to maintain power delivered to the residence approximately below the preselected peak limit while hopefully causing a minimum amount of inconvenience to the residential customer.
Experience has shown that complex controllers have certain disadvantages. One disadvantage is that some residential customers "tinker" with the control panel settings so frequently that the purpose of the energy controller is often defeated because the user occasionally by-passes the originally set peak power limit, causing the controller to allow a very high amount of peak power to be delivered to the controlled loads. This results in a high billing rate for the entire billing period during which the control panel was tinkered with. The customer is likely to be dissatisfied with the operation of the controller because it does not save him any money but does cause him some inconvenience.
It has been found that the hardware used in implementing the above-mentioned control panels is very expensive, and constitutes a substantial portion of the total hardware cost of some prior residential energy controllers.
The present assignee's experience in testing energy controllers seems to suggest that peak power consumption by many residential customers, in summer months, at least, is determined mainly by only a few controlled loads, namely, the air conditioner, the hot water heater, and in some cases, a swimming pool filter pump. Numerous remaining appliances frequently operated in most residences, such as dishwashers, washing machines, electric lights, vacuum cleaners, etc. frequently have a very minor impact on the peak power usage pattern for that residence, indicating that in many cases the peak power usage would be essentially uneffected even if these other appliances are not controlled by a residential energy controller.
Testing and simulation experiments with various shed/restore algorithyms have suggested that such algorithyms often result in unexpected or anamalous behavior when used in residences for a long period of time. For example, some algorithyms result in an excessive amount of switching of controlled loads. Since excessive switching of most electrical appliances can reduce their useful life and may also be very inconvenient to the residential customer, this excessive switching is obviously undesirable. In some instances it has been found that certain controlled loads are rarely switched off by the controller, and in other instances, low priority loads may be switched off by the controller but rarely switched back on.
In most residences, there are a number of unpredictable, temporary sharp increases in the amount of energy required by that residence. For example, overnight visits by a large number of guests may cause some energy controller algorithyms to operate in a manner that is highly inconvenient to the residential customer.
For many residential customers, it appears that a more simplified approach to residential energy control to prevent excessively high peak power consumption while causing minimum impact on the residential users lifestyle is needed. One known device attempts to accomplish this objective by providing a simple "interlock" device which automatically disconnects the water heater every time the air conditioner is turned on by the thermostat sensing room temperature within the residence. However, this approach is believed to be overly simplified. Even though advantageous operation may be achieved by this device under summer conditions wherein a predetermined peak power limit will be exceeded every time the air conditioner is turned on, it may be desirable in some instances to have a load control that turns both the air conditioning unit and the hot water heater off when the power consumed by other loads exceeds a certain level. The above described interlock device cannot perform this function. Obviously, the above-mentioned interlock device is essentially useless during the winter months in a home that does not utilize the same unit (i.e., a heat pump) both to heat and cool the residence.
Thus, the air conditioner/water heater interlock device fails in many instances to achieve the desired objectives of minimizing peak power consumption of the residence while also minimizing inconvenience to the user while keeping the total cumulative energy consumption at normal levels.
The present assignee's experimental results also suggest that a fixed maximum peak load limit that, if exceeded, causes shedding of loads can cause highly ineffective use of energy controllers during portions of the year when it is unlikely that high peak power consumption will occur even if no energy controller is used at all. For example, in a home heated by natural gas, excessive peaking of power consumption normally will occur only in the summer. For example, assume that in such a home an energy controller begins shedding controlled loads at predetermined demand limit of eight kilowatts in the summer when total power consumption with the air conditioning unit is turned on. It is quite likely that the energy controller will never shed any load during the winter months. Consequently, during the winter, no benefit is obtained by the residential customer from the energy controller. Nevertheless, peaking of the residence power consumption does occur, albeit at lower levels in the winter for such a residence, and such peaking may occur within a price-sensitive power range. Any time substantial peaking of power consumption by a residence occurs within a price-sensitive power range, there is an opportunity for savings on the energy billing rate if some power usage during the peaking period can be postponed. Therefore, if prioritized load shedding and load restoring operations are effected, a reduced rate for that residential consumer can result, and this reduced rate can be achieved with minimum inconvenience to him if the energy controller is properly designed.
Several prior art references, including U.S. Pat. No. 2,874,310; U.S. Pat. No. 3,970,861; 4,135,101 disclose use of bi-metal temperature sensitive elements that are heated in response to the total amount of power output from a typical power distribution transformer in a residential neighborhood. When the total output power reaches a certain level, the temperature sensitive bi-metal element (which is gradually deflected as a function of its increased temperature) actuates a switch. The actuation of the switch results in signals that are utilized to energize motors that drive cams which, in turn, cyclically turn controlled loads off and on to reduce the peak power consumed by loads served by the transformer. The devices disclosed in the three foregoing references do not provide any adjustment in the temperature setting of thermostats that control switching of the air conditioning units or heating units, both of which may be responsible for a major portion of the power demand of a particular residential customer, and both of which may greatly impact the comfort and lifestyle of the residential user if "mismanaged" by an automatic energy controller.
It can be seen that despite all of the research and development that has occurred in the field of residential energy controllers in recent years, there still remains an unfulfilled need for a low cost, highly reliable "tinker-proof" automatic energy controller that substantially reduces peak power consumption by a residence without substantial inconvenience to the residential user, thereby reducing energy billing rates for that user without unacceptable impact upon his lifestyle.
Therefore, it is an object of the invention to provide an energy controller system and method that avoid the high cost and the great complexity of structure and operation of many prior energy controllers, especially those utilizing processors to control load shedding and restoring operations.
It is another object of the invention to provide an energy controller and method that automatically seasonally varies peak power consumption limits which, if exceeded by the residence, cause shedding of controlled loads.
It is another object of the invention to provide an energy controller and method which result in avoidance of increased electric utility power rates for a billing period based on peak power consumption during that billing period, and which avoid increased electric utility power billing throughout the year.
It is another object of the invention to provide an energy controlling system and method that automatically varies the setting of a thermostat in accordance with the amount of power being delivered to a residence or establishment.